Blue Hauler, Caampeeee and Wagit got it right............if it ain't on the MR, then IT AIN'T ON! end of story. If your maintenance is being done under some other approved arrangement, then it will be reflected on the MR accordingly. This chap said the MR expired at x-date and x-time and the time was due up in 4 hours....then the MR expires in 4 hours.
I personally know of a parachute operation that overran the MR by 40 (YES, FORTY) hours and convinced the pilot that because they hadn't been making entries onto the MR for the past 2 weeks, then all was legit and above-board.
Funnily enough, the maintenance organisation had a slightly different view and issued the new MR with an expiry time of only 60 hours!
Risked everybody's licences for absolutely nothing.....except a big law suit had everything turned to custard.
Funny thing; they're still in business today.